Slurry Composition And Method For Polishing Organic Polymer-Based Ophthalmic Substrates

ABSTRACT

The present invention provides a slurry composition and method for polishing organic polymer-based ophthalmic substrates. The slurry composition according to the invention includes an aqueous dispersion of abrasive particles and a pyrrolidone compound. The abrasive particles can be alumina, zirconia, silica, titania or combinations of the foregoing. Slurry compositions according to the invention can be used to polish all types of organic polymer-based ophthalmic substrates, but are particularly useful for polishing organic polymer-based ophthalmic substrates having an index of refraction greater than 1.498 because they remove such materials at a greater efficiency than conventional slurry compositions without detrimentally affecting the quality of the resulting surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.11/102,555, filed Apr. 8, 2005.

BACKGROUND OF INVENTION

1. Field of Invention

The present invention relates to a slurry composition and method forpolishing organic polymer-based ophthalmic substrates.

2. Description of Related Art

A variety of slurry compositions are known in the art for use inpolishing organic polymer-based ophthalmic substrates. Such prior artslurry compositions generally consist of abrasive particles dispersed indeionized water and/or other liquids. Commonly utilized abrasiveparticles include, for example, cerium oxide, aluminum oxide, zirconiumoxide, tin oxide, silicon dioxide and titanium oxide. Aluminum oxideslurry is most commonly used for polishing organic polymer-basedophthalmic substrates such as, for example, allyl diglycol carbonatepolymer, which is commonly known in the art as CR-39, and other higherindex of refraction polycarbonate resins.

Slurry compositions consisting solely of aluminum oxide abrasiveparticles dispersed in deionized water produce acceptable surfacequality when used to polish organic polymer-based ophthalmic substrates,but exhibit unacceptably low polishing efficiency (i.e., a low removalrate). The polishing efficiency of such slurry compositions can beimproved by using significantly larger aluminum oxide particles, but theuse of larger particles results in unsatisfactory surface quality (i.e.scratches, pit marks, orange peel or like defects).

Koshiyama et al., U.S. Pat. No. 4, 225,349, disclose a polishingcomposition consisting of calcined alumina (aluminum oxide particles)and an aluminum salt polishing accelerator dispersed in deionized waterthat accelerates the removal of the CR-39 substrate material withoutdegrading the surface quality. The preferred polishing acceleratoridentified by Koshiyama et al. is aluminum nitrate.

CR-39, which has an index of refraction of about 1.498, has dominatedthe market for organic polymer-based ophthalmic substrates for manyyears. In recent years, however, higher index of refraction organicpolymer-based ophthalmic substrates have been developed, and thesehigher index of refraction substrates are becoming more prevalent in theophthalmic lens market. The higher index of refraction substratesprovide several distinct advantages over CR-39 in ophthalmic lensapplications. For example, lenses that are fabricated from 1.586 indexof refraction polycarbonate substrates are thinner and lighter in weightthan comparable lenses fabricated from CR-39, and further provideimproved impact resistance. This makes polycarbonate-based ophthalmicsubstrates more suitable for use in fabricating eyewear worn bychildren, active adults and in the production of safety glasses.Generally speaking, the higher the index of refraction, the thinner andlighter the ophthalmic lens. Higher index of refraction organicpolymer-based ophthalmic substrates allow for the fabrication of eyewearthat is functional and fashionable, and which eliminates the “bulbous”or thick “coke-bottle” look often found with lower index of refractionlenses.

Known slurry compositions for use in polishing CR-39 do not provide thedesired polishing efficiency, even when a conventional accelerator suchas aluminum nitrate is present. A slurry composition that provides highremoval efficiency, particularly on higher index of refraction organicpolymer-based ophthalmic substrates, is desired.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a slurry composition and method forpolishing organic polymer-based ophthalmic substrates. The slurrycomposition and method of the invention polishes high indexpolymer-based ophthalmic substrates with greater polishing efficiencyand surface quality than can be achieved with conventional slurrycompositions. A slurry composition according to the invention comprisesan aqueous dispersion of abrasive particles and a pyrrolidone compound.The abrasive particles can be alumina, zirconia, silica, titania orcombinations of the foregoing. Slurry compositions according to theinvention can be used to polish all types of organic polymer-basedophthalmic substrates, but are particularly useful for polishing organicpolymer-based ophthalmic substrates having an index of refractiongreater than 1.498 because they remove such materials at a greaterefficiency than conventional slurry compositions without detrimentallyaffecting the quality of the resulting surface.

The foregoing and other features of the invention are hereinafter morefully described and particularly pointed out in the claims, thefollowing description setting forth in detail certain illustrativeembodiments of the invention, these being indicative, however, of but afew of the various ways in which the principles of the present inventionmay be employed.

DETAILED DESCRIPTION OF THE INVENTION

Throughout the instant specification and in the appended claims, thephrase “organic polymer-based ophthalmic substrates” refers to organicthermosetting or thermoplastic polymer materials used in the fabricationof eyeglass lenses and other optometric devices. Included within thisdefinition are polycarbonate materials such as allyl diglycol carbonatepolymers commonly known as CR-39 and other thermosetting andthermoplastic organic polymer resins used to fabricate ophthalmiclenses. Specifically excluded from this definition are inorganic glassesand inorganic crystal based substrates. The phrase “high index organicpolymer-based ophthalmic substrates” refers to those organicpolymer-based ophthalmic substrates that have an index of refractiongreater than 1.498, which is the index of refraction for the allyldiglycol carbonate polymer known in the art as CR-39. Most manufacturersof organic polymer-based ophthalmic substrates regard the specificcomposition of their ophthalmic substrate materials as proprietaryinformation. Applicants do not have knowledge of the specificcompositions of such materials, but generally know that such substratesbelong to polymer families such as polycarbonates, polyurethanes,polyesters including polyacrylates and epoxies, polyacrylamides andpolysulfones. These organic polymer families may be homopolymers orcopolymers, and many are cross-linked and/or co-polymerized with otherorganic and inorganic compounds. Most are thermocast.

Slurry compositions according to the present invention can be used topolish all organic polymer-based ophthalmic substrates, but areparticularly suitable for use in polishing high index organicpolymer-based ophthalmic substrates. As shown in the accompanyingExamples, slurry compositions according to the invention provide greaterpolishing efficiency on high index organic polymer-based ophthalmicsubstrates than convention slurry compositions. Furthermore, slurrycompositions according to the invention provide similar, if notimproved, polishing efficiencies on traditional polycarbonate materialssuch as CR-39. In all applications, slurry compositions according to theinvention provide acceptable surface quality.

Slurry compositions according to the present invention preferablycomprise an aqueous dispersion comprising abrasive particles and apyrrolidone compound. The abrasive particles must be selected from thegroup consisting of alumina, zirconia, silica, titania and combinationsof the foregoing. It will be appreciated that the abrasive particles canbe doped with or contain small amounts of other elements. Abrasives aretypically produced by high temperature calcination, but can be producedby other methods. Calcined alumina abrasive particles are presently mostpreferred for use in the invention.

The abrasive particles used in the invention preferably have a particlesize within the range of from about 0.01 μm to about 4.0 μm, morepreferably within the range of from about 0.05 μm to about 2.5 μm, andmost preferably within the range of from about 1.0 μm to about 2.5 μm.The abrasive particles preferably comprise from about 5% to about 40% ofthe slurry composition by weight, and more preferably within the rangeof from about 10% to about 30% of the slurry composition by weight.

A preferred pyrrolidone compound for use in the invention is polyvinylpyrrolidone (“PVP”). Preferably, the weight average molecular weight ofthe PVP used in the slurry composition according to the invention iswithin the range of from about 3,000 to about 60,000, and morepreferably from about 10,000 to about 50,000. PVP with a weight averagemolecular weight within these ranges is readily available from a varietyof chemical suppliers.

It will be appreciated that the pyrrolidone compound need not be PVP.Other pyrrolidone compounds, such as N-octyl-2-pyrrolidone,N-dodecyl-2-pyrrolidone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone,N-hydroxyethyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone,N-butyl-2-pyrrolidone, N-hexyl-2-pyrrolidone, N-decyl-2-pyrrolidone,N-octadecyl-2-pyrrolidone, N-hexadecyl-2-pyrrolidone and copolymers ofpolyvinyl pyrrolidone, and combinations of the foregoing can also beused. Polyvinyl caprolactam can be used as an alternative to apyrrolidone compound.

The pyrrolidone compound is preferably present in the slurry compositionat a loading of from about 0.025% to about 5% by weight, and morepreferably from about 0.1 5% to about 4.0% by weight. The effectivenessof the pyrrolidone compound in increasing the removal efficiency of highindex organic polymer-based ophthalmic substrates is not diminished whenconventional accelerators such as aluminum nitrate are also present.

Aluminum nitrate is a known polishing efficiency accelerator for use on1.498 Index substrates. Aluminum nitrate can be used in slurrycompositions according to the invention without adversely degrading theefficiency improvements provided on high index organic polymer-basedophthalmic substrates. When aluminum nitrate is used in a slurrycomposition according to the invention, it is present in an amountpreferably within the range of from about 0.25% to 4.0% by weight, andmore preferably from about 0.5% to about 3.0% by weight.

As is well known in the art, colloidal aluminum hydroxide can be used asa suspending agent for alumina abrasive particles. When present, thecolloidal aluminum hydroxide comprises from about 0.49% to about 1.47%by weight of the slurry, and more preferably, 0.735% to about 1.225% byweight of the slurry.

Preferably, an anti-foaming agent such as modified siloxane treatedfumed silica is also used. Anti-foaming agents of this type are wellknown in the art, and can be acquired from a variety of vendors.Anti-foaming agents are typically present in an amount from about 0.025%to about 0.30% by weight, and more preferably from about 0.025% to about0.10% by weight.

The slurry composition according to the present invention is preferablyaqueous in nature, meaning that the individual components of the slurryare dispersed in deionized water. However, other liquid polishing mediacan be used.

It will be appreciated that surfactants, biocides, pH modifiers, pHbuffers, rheology modifiers and other compounds can also be present inthe slurry composition provided they do not adversely react with theabrasive particles and/or the pyrrolidone compound and thereby adverselyaffect the efficiency of the polishing slurry, or detrimentally affectthe final surface quality produced via polishing.

It will be appreciated that the slurry composition can be shipped andstored in the form of a dry powder or concentrated aqueous paste, whichcan be readily dispersed in water with a minimum of mixing in order toprepare an aqueous polishing slurry for polishing organic polymer-basedophthalmic substrates. Thus, the invention further provides a dry powdercomposition that can be dispersed in water to form an aqueous polishingslurry, and a method of polishing an organic polymer-based ophthalmicsubstrate comprising dispersing a composition comprising abrasiveparticles selected from the group consisting of alumina, zirconia,silica and titania and a pyrrolidone compound and/or polyvinylcaprolactam in water to form an aqueous polishing slurry, disposing theaqueous polishing slurry between a polishing pad and the organicpolymer-based ophthalmic substrate, and polishing the organicpolymer-based ophthalmic substrate with the polishing pad and theaqueous polishing slurry to remove a surface portion of the organicpolymer-based ophthalmic substrate.

The following examples are intended only to illustrate the invention andshould not be construed as imposing limitations upon the claims.

EXAMPLES

In the following examples, unless otherwise stated, the term “Alumina”refers to calcined aluminum oxide having an average particle size ofabout 1.0 pm to about 2.5 pm. The term “Aluminum Hydroxide” refers tocolloidal aluminum hydroxide (˜90 nm Boehmite) dispersed in water, butis reported in the tables as a dry weight equivalent. The term “AluminumNitrate” refers to a solution of aluminum nitrate dissolved in water,but is reported in the tables as a dry weight equivalent. The term“Antifoam” refers to a modified siloxane treated fumed silica. The term“PVP-3,500 Mw” refers to a polyvinyl pyrrolidone polymer having a weightaverage molecular weight of about 3,500. The term “PVP-10,000 Mw” refersto a polyvinyl pyrrolidone polymer having a weight average molecularweight of about 10,000. The term “PVP-29,000 Mw” refers to a polyvinylpyrrolidone polymer having a weight average molecular weight of about29,000. The term “PVP-55,000 Mw” refers to a polyvinyl pyrrolidonepolymer having a weight average molecular weight of about 55,000.

The organic polymer-based ophthalmic substrates tested in the followingexamples are referred to by their refractive index. The specificcompositions of the organic polymer-based ophthalmic substrates areregarded as proprietary by the manufacturers, and are not known byapplicant. The term “1.498 Index” refers to an organic polymer-basedophthalmic substrate (believed to comprise an allyl diglycol carbonatepolymer), which can be obtained from Essilor of America, Inc. ofPetersburg, Fla. as CR-39. The term “1.55 Index” refers to an organicpolymer-based ophthalmic substrate (believed to comprise vinyl allylester oligomers), which can be obtained from Younger Optics of Torrance,Calif., and is available commercially as EASY-LITE 1.55. The term “1.586Index” refers to an organic polymer-based ophthalmic substrate (believedto comprise a polycarbonate polymer), which can also be obtained fromEssilor of America, Inc. The term “1.60 Index” refers to an organicpolymer-based ophthalmic substrate (believed to comprise a blend ofpolyurethane polymer and sulfur), which can be obtained from the SilorDivision of Essilor of America, Inc. as available as THIN & LITE 1.60.The term “1.74 Index” refers to an organic polymer-based ophthalmicsubstrate (believed to comprise a polyurethane/sulfur blend or apolyurethane/polysulfone blend), which can be obtained from Miki & Co.,Ltd. of Tokyo, Japan as 1.74 HI INDEX.

Example 1

Slurries 1A through 1E were each separately formed by mixing togetherthe amounts of the Components shown in weight percent in Table 1. Afterthe slurries were formulated, measurements of the pH and the viscositywere made, and the data is reported in Table 1 below. A fresh amount ofeach slurry formulation was used to polish the organic polymer-basedophthalmic substrates listed in the “REMOVAL RATE” section of Table 1.The organic polymer-based ophthalmic substrates were separately polishedon a Coburn 505 Optical Polisher equipped with a bowl type slurryreservoir. The polishing pad was a SHAWSHEEN 349-7 Premium Grade YellowPolishing Pad obtained from PSI of Odessa, Fla. The Optical Polishermachine settings were 20.0 psi pressure and 742 RPM. The reservoir wasequipped with a small recirculating pump. The slurry reservoir wascharged with a fresh two thousand gram supply of slurry for eachpolishing test. The slurry was recirculated at a flow rate of 4.54liters/minute. The slurry was chilled throughout each polishingexperiment to a temperature range of 10 to 15° C. The substrates werenot fined between polishing cycles. Polishing efficiency was determinedby measuring the weight loss of each substrate after each polishingcycle and is reported in Table 1 as weight loss in milligrams per6-minute cycle. The weight loss values reported in Table 1 were obtainedvia polishing each substrate three times, and then averaging the weightloss for the three polishing cycles. TABLE 1 Slurry Slurry Slurry SlurrySlurry 1A 1B 1C 1D 1E COMPONENTS: Deionized Water 89.95 87.79 89.4589.45 89.45 Alumina 10.00 10.00 10.00 10.00 10.00 Antifoam 0.05 0.050.05 0.05 0.05 Aluminum Nitrate — 2.16 — — — PVP - 10,000 M_(w) — — 0.50— — PVP - 3,500 M_(w) — — — 0.50 — PVP - 55,000 M_(w) — — — — 0.50PHYSICAL DATA: pH 10.04 3.64 9.89 9.96 9.88 Viscosity (cps) 3.40 3.9022.60 37.50 24.80 REMOVAL RATE: 1.498 Index 98 138 104 58 63 (mg/6 min)1.586 Index 36 43 53 62 68 (mg/6 min) 1.55 Index (mg/6 min) 147 186 257230 242 1.60 Index (mg/6 min) 81 87 131 111 107 1.74 Index (mg/6 min)108 150 280 274 255

Slurries 1C, 1D and 1E, which included 0.5% by weight of a polyvinylpyrrolidone exhibited an increased polishing efficiency as compared toSlurry 1A, which did not contain any polyvinyl pyrrolidone and Slurry B,which contained a conventional loading of a known alumina polishing rateaccelerator, aluminum nitrate. Slurries 1C, 1D and 1E also demonstratethat the increase in polishing efficiency occurs using various molecularweights of polyvinyl pyrrolidone.

Example 2

Slurries 1F through 1I were each separately formed by mixing togetherthe amounts of the Components shown in weight percent in Table 2. Afterthe slurries were formulated, measurements of the pH and the viscositywere made, and the data is reported in Table 2 below. A fresh amount ofeach slurry formulation was used to polish the organic polymer-basedophthalmic substrates using the same procedures and polishing equipmentas described in Example 1. The polishing rate removal efficiency isreported in Table 2 below: TABLE 2 Slurry Slurry Slurry Slurry SlurrySlurry 1A 1B 1F 1G 1H 1I COMPO- NENTS: Deionized 89.95 87.84 89.92589.80 87.95 85.95 Water Alumina 10.00 10.00 10.00 10.00 10.00 10.00Antifoam 0.05 0.05 0.05 0.05 0.05 0.05 Aluminum — 2.16 — — — — NitratePVP - — — 0.025 0.15 2.00 4.00 10,000 M_(w) PHYSICAL DATA: pH 10.04 3.649.13 X 6.87 5.99 Viscosity 3.40 3.90 26.90 X 3.40 2.90 (cps) REMOVALRATE: 1.498 98 138 59 X 77 109 Index (mg/6 min) 1.586 36 43 58 X 56 59Index (mg/6 min) 1.55 147 186 155 223 275 309 Index (mg/6 min) 1.60 8187 59 113 136 155 Index (mg/6 min) 1.74 108 150 172 X 219 227 Index(mg/6 min)X means that no test data is available

In Slurry 1F, a 0.025 weight percent loading of a 10,000 weight averagemolecular weight polyvinyl pyrrolidone showed a modest increase inpolishing efficiency for 1.586 Index and 1.74 Index substrates,respectively, as compared to the polishing efficiencies obtained inExample 1 for Slurries 1A and 1B. However, at this loading, no increasein polishing efficiency was obtained for the 1.55 Index and 1.60 Indexsubstrate. In Slurry, 1G, the polyvinyl pyrrolidone loading wasincreased to 0.15 weight percent. Slurry 1G was used to polishsubstrates 1.55 Index and 1.60 Index only, and was shown to increase thepolishing efficiency for such substrates. Slurries 1G, 1H and 1I eachdemonstrated a higher rate of polishing efficiency for all substrateswith an index of refraction greater than 1.498.

Example 3

Slurries 2A, 2B and 2C were each separately formed by mixing togetherthe amounts of the Components shown in weight percent in Table 3. Afterthe slurries were formulated, measurements of the pH and the viscositywere made, and the data is reported in Table 3 below. A fresh amount ofeach slurry formulation was used to polish the organic polymer-basedophthalmic substrates using the same procedures and polishing equipmentas described in Example 1. The polishing rate removal efficiency isreported in Table 3 below: TABLE 3 Slurry 2A Slurry 2B Slurry 2CCOMPONENTS: Deionized Water 79.95 77.79 79.45 Alumina 20.00 20.00 20.00Antifoam 0.05 0.05 0.05 Aluminum Nitrate — 2.16 — PVP - 29,000 M_(w) — —0.50 PHYSICAL DATA: pH 10.35 3.70 9.88 Viscosity (cps) 19.00 6.40 146.50REMOVAL RATE: 1.498 Index 129 181 129 (mg/6 min) 1.586 Index 47 61 69(mg/6 min) 1.55 Index (mg/6 min) 236 269 297 1.60 Index (mg/6 min) 108131 150

Example Slurry 2C, which contains a polyvinyl pyrrolidone, clearlydemonstrates the increased polishing efficiency obtained for substrateswith an index of refraction greater than 1.498 as compared to Slurry 2A,which contained no polishing accelerator, and Slurry 2B, which containeda conventional loading of a conventional aluminum nitrate polishing rateaccelerator.

Example 4

Slurries 3A, 3B and 3C were each separately formed by mixing togetherthe amounts of the Components shown in weight percent in Table 4. Afterthe slurries were formulated, measurements of the pH and the viscositywere made, and the data is reported in Table 4 below. A fresh amount ofeach slurry formulation was used to polish the organic polymer-basedophthalmic substrates using the same procedures and polishing equipmentas described in Example 1. The polishing rate removal efficiency isreported in Table 4 below: TABLE 4 Slurry 3A Slurry 3B Slurry 3CCOMPONENTS: Deionized Water 69.95 67.79 69.45 Alumina 30.00 30.00 30.00Antifoam 0.05 0.05 0.05 Aluminum Nitrate — 2.16 — PVP - 29,000 M_(w) — —0.50 PHYSICAL DATA: pH 10.13 3.69 10.35 Viscosity (cps) 747.80 7.80105.00 REMOVAL RATE: 1.498 Index 148 188 153 (mg/6 min) 1.586 Index 4265 72 (mg/6 min) 1.55 Index (mg/6 min) 284 309 349 1.60 Index (mg/6 min)129 147 182

Example Slurry 3C, which contains a polyvinyl pyrrolidone, clearlydemonstrates the increased polishing efficiency obtained for substrateswith an index of refraction greater than 1.498 as compared to Slurry 3A,which contained no polishing accelerator, and Slurry 3B, which containeda conventional Aluminum Nitrate polishing rate accelerator.

Example 5

Slurries 4A and 4B were each separately formed by mixing together theamounts of the Components shown in weight percent in Table 5. After theslurries were formulated, measurements of the pH and the viscosity weremade, and the data is reported in Table 5 below. TABLE 5 Slurry 4ASlurry 4B COMPONENTS: Deionized Water 80.11 80.61 Alumina 16.50 16.50Aluminum Nitrate 1.98 1.98 Aluminum Hydroxide 0.86 0.86 PVP - 10,000M_(w) 0.50 — Antifoam 0.05 0.05 PHYSICAL DATA: pH 3.58 3.64 Viscosity(cps) 42.0 31.9

Slurry 4A, Slurry 4B (a non-PVP containing control slurry) and aconventional plastic lens polishing slurry commercially available asPRAXAIR H-A1 (pH 3.3; viscosity 50+cps), were each separately used topolish “1.498 Index” and “1.586 Index” substrates (lenses). All lenseswere polished on a LOH Optical TORO-X2 Polisher. The polishing pad was aSHAWSHEEN 349-7 Premium Grade Yellow Polishing Pad obtained from PSI ofOdessa, Fla. The machine settings were 0.35 bar pressure and 908 RPM.Four thousand grams of slurry were used for each experiment. Each slurrywas contained in a two-gallon container equipped with a high-speedagitator/pump that was used to recirculate the slurry through thepolishing chamber and back into the slurry containment vessel. Theslurry was recirculated at a flow rate of 1.0 gallon per minute. Theslurry was chilled throughout each polishing experiment to a temperaturerange of 10-15° C. Additional polishing slurry was not added betweencycles to make up for any slurry loss due to polish drag out. Polishingefficiency was determined by measuring the average weight loss of eachpair of lenses after each polishing cycle and is reported in Table 6 asmg loss per 6-minute cycle. Each slurry was evaluated by polishing tenpairs each of 1.498 Index and 1.586 Index lenses. Polishing cyclesalternated between 1.498 Index substrates and 1.586 Index substrates.The substrates were not fined between polishing cycles. TABLE 6 1.498Index 1.586 index Slurry Slurry Praxair Slurry Slurry Praxair 4A 4B H-A14A 4B H-A1 Cycle 1 175 155 150 79 52 60 Cycle 2 177 155 128 73 49 64Cycle 3 180 168 126 77 54 60 Cycle 4 178 163 129 72 59 56 Cycle 5 178166 126 69 56 58 Cycle 6 179 167 128 72 56 62 Cycle 7 183 168 127 76 5659 Cycle 8 175 160 122 71 51 60 Cycle 9 172 164 124 68 58 59 Cycle 179162 126 74 54 57 10

Example 5 demonstrates that Slurry A, which contained a pyrrolidonecompound, consistently exhibited a higher polishing efficiency thaneither comparison Slurry B (same formulation, except no PVP) and thecommercially available plastic lens polishing slurry, and did so forboth the 1.498 Index and 1.586 Index substrates.

Example 6

Slurry 4C was formed by mixing together the amounts of the componentsshown in weight percent in Table 7 below: TABLE 7 Components Weight %Deionized Water 80.60 Alumina 16.00 Aluminum Nitrate 1.98 AluminumHydroxide 0.86 PVP- 10,000 Mw 0.50 Antifoam 0.05

Slurry 4C was then dried to a powder and redispersed in deionized waterto form the reconstituted slurry 4D. The pH and viscosity of slurry 4Dwere measured and the results are reported in Table 8. TABLE 8 PhysicalData pH 4.4 Viscosity (cps) 3.4

The dry powder was formed by spray drying the slurry 4C with a NiroMobile Minor Pilot Scale Spray Dryer. Drying of such slurry formulationsis not limited to this method and can be achieved by other conventionalmeans such as tray drying in a convection oven. The dry powder wasredispersed in deionized water (711.6 g dry powder and 3288.4 gdeionized water) to form the reconstituted slurry 4D. The powder can beeasily dispersed with minimum agitation required. For amounts such asthat described above simply combining the components in a gallon jug,capping the jug with a tight fitting lid and shaking for several minutesis sufficient to redisperse the powder into a useable polish. Largerbatches of material can be combined in any suitable vessel and stirringthe contents with a portable mixer such as a lab mixer or paint typemixer attached to a portable hand held drill. Larger batches can also behand stirred with a large spatula or other similar stirring device.Water other than deionized water (i.e. tap water) can be used toredisperse the dried powder.

The incorporation of PVP (polyvinyl pyrrolidone) into the formulationfacilitates the rapid and complete-dispersing of the powder. Themechanism for this rapid and complete redispersion of the dried powderis believed to be the result of PVP's ability to disintegrate driedpowder agglomerates.

Example 7

Both slurries 4C and 4D were used to polish 1.498 Index, 1.586 Index,1.55 Index, 1.60 Index, 1.67 Index and 1.74 Index substrates (lenses).All lenses were polished on a LOH Optical TORO-X2 polisher. Thepolishing pad was a SHAWSHEEN 349-7 Premium Grade Yellow Polishing Padobtained from PSI of Odessa, Fla. The machine settings were 0.35 barpressure and 908 RPM. Four thousand grams of each slurry was used forthis experiment. The slurry was contained in a two-gallon containerequipped with a high-speed agitator/pump that was used to recirculatethe slurry through the polishing chamber and back into the slurrycontainment vessel. The slurry was recirculated at a flow rate of 1.0gallon per minute. The slurry was chilled throughout the polishingexperiment to a temperature range of 10-15° C. Additional polishingslurry was not added between cycles to make up for any slurry loss dueto polish drag out. The removal was determined by measuring the averageweight loss of each pair of lenses during each polishing cycle and isreported in Table 9 as mg loss per 6-minute cycle. Each slurry wasevaluated by polishing twelve pairs each of 1.498 Index and 1.586 Indexlenses. Polishing cycles alternated between 1.498 Index substrates and1.586 Index substrates. The substrates were not fined between polishingcycles. The removal data during each polishing cycle for these slurriesare listed in Table 9. Indices of 1.55, 1.60, 1.67 and 1.74 lenses wereonly polished at polishing Cycle 1 and again at polishing Cycle 12 andthe removals are listed in Table 10.

Example 7 demonstrates that reconstituted slurry 4D exhibited acomparable polishing rate performance to the original slurry 4C for lenssubstrates with indices higher than 1.498. The reconstituted slurry 4Ddid show a reduced polishing rate for 1.498 Index substrate whencompared to polishing the original slurry 4C. Surface quality of alllenses polished with reconstituted slurry 4D showed no detrimentaleffects or reduction in surface quality when compared with thecorresponding index lens polished with the original slurry 4C. TABLE 91.498 1.586 1.498 Index Index 1.586 Index Index Polishing ReconstitutedOriginal Reconstituted Original Cycle Slurry 4D Slurry 4C Powder 4DSlurry 4C 1 155 210 78 74 2 142 191 71 76 3 145 189 69 71 4 140 188 6471 5 145 189 66 74 6 145 187 70 71 7 145 179 64 76 8 139 176 67 70 9 136182 64 69 10 135 188 66 68 11 129 178 66 68 12 124 189 67 67

TABLE 10 1.55 1.60 1.67 1.74 Index Index Index Index ReconstitutedSlurry 469 185 239 389 4D, Cycle 1 Reconstituted Slurry 419 175 217 3644D, Cycle 12 Original Slurry 4C, 399 198 238 388 Cycle 1 Original Slurry4C, 417 170 222 353 Cycle 12

additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and illustrative examples shown anddescribed herein. Accordingly, various modifications may be made withoutdeparting from the spirit or scope of the general inventive concept asdefined by the appended claims and their equivalents.

1. A method of polishing an organic polymer-based ophthalmic substratecomprising: dispersing a composition comprising abrasive particlesselected from the group consisting of alumina, zirconia, silica andtitania and a pyrrolidone compound and/or polyvinyl caprolactam in waterto form an aqueous polishing slurry; disposing the aqueous polishingslurry between a polishing pad and the organic polymer-based ophthalmicsubstrate; and polishing the organic polymer-based ophthalmic substratewith the polishing pad and the aqueous polishing slurry to remove asurface portion of the organic polymer-based ophthalmic substrate. 2.The method according to claim 1 wherein the organic polymer-basedophthalmic substrate is a high index organic polymer-based ophthalmicsubstrate.
 3. The method according to claim 1 wherein the abrasiveparticles have an average particle size of from about 0.01 μm to about4.0 μm.
 4. The method according to claim 3 wherein the abrasiveparticles have an average particle size of from about 1.0 μm to about2.5 μm.
 5. The method according to claim 1 wherein the compositioncomprises a polyvinyl pyrrolidone having a weight average molecularweight of from about 3,000 to about 60,000.
 6. The method according toclaim 5 wherein the composition comprises a polyvinyl pyrrolidone havinga weight average molecular weight of from about 1 0,000 to about 50,000.7. The method according to claim 1 wherein the composition comprises apyrrolidone compound and after the composition is dispersed in water,the pyrrolidone compound comprises from about 0.025% to about 5% of theaqueous polishing slurry by weight.
 8. The method according to claim 7wherein after the composition is dispersed in water, the pyrrolidonecompound comprises from about 0.1 5% to about 4% of the aqueouspolishing slurry composition by weight.
 9. The method according to claim1 wherein the composition comprises a pyrrolidone compound selected fromthe group consisting of N-octyl-2-pyrrolidone, N-dodecyl-2-pyrrolidone,N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone,N-hydroxyethyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone,N-butyl-2-pyrrolidone, N-hexyl-2-pyrrolidone, N-decyl-2-pyrrolidone,N-octadecyl-2-pyrrolidone, N-hexadecyl-2-pyrrolidone and copolymers ofpolyvinyl pyrrolidone, and combinations of the foregoing.
 10. The methodaccording to claim 1 wherein the abrasive particles consist essentiallyof alumina.
 11. The method according to claim 1 wherein the compositioncomprises a polyvinyl pyrrolidone having a weight average molecularweight of from about 10,000 to about 50,000
 12. The method according toclaim 1 wherein the composition is in the form of a dry powder before itis dispersed in water.
 13. The method according to claim 1 wherein thecomposition is in the form of an aqueous paste before it is dispersed inwater.
 14. A dry powder composition consisting essentially of: (I)abrasive particles; (II) a pyrrolidone compound and/or polyvinylcaprolactam; and optionally, (III) aluminum nitrate, suspending agents,and/or antifoaming agents; wherein the dry powder composition isdispersible in water to form an aqueous polishing slurry for use inpolishing organic polymer-based ophthalmic substrates.
 15. The drypowder composition according to claim 14 wherein the abrasive particlesconsist essentially of alumina.
 16. The dry powder composition accordingto claim 15 wherein the alumina abrasive particles have an averageparticle size of from about 0.01 μm to about 4.0 μm.
 17. The dry powdercomposition according to claim 14 wherein the dry powder compositioncomprises a polyvinyl pyrrolidone having a weight average molecularweight of from about 3,000 to about 60,000.
 18. The dry powdercomposition according to claim 14 wherein the dry powder compositioncomprises a pyrrolidone compound selected from the group consisting ofN-octyl-2-pyrrolidone, N-dodecyl-2-pyrrolidone, N-methyl-2-pyrrolidone,N-ethyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone,N-cyclohexyl-2-pyrrolidone, N-butyl-2-pyrrolidone,N-hexyl-2-pyrrolidone, N-decyl-2-pyrrolidone, N-octadecyl-2-pyrrolidone,N-hexadecyl-2-pyrrolidone and copolymers of polyvinyl pyrrolidone, andcombinations of the foregoing.